window.onunhandledrejection called twice

[clemp6r]

Hi, in a browser environment, we have a callback defined as:

window.onunhandledrejection = ...

In case of unhandled promise rejection, our callback is called twice.
We inspected core-js source code and the problem seems to be in es.promise.js:

var dispatchEvent = function (name, promise, reason) {
  var event, handler;
  if (DISPATCH_EVENT) {
    event = document.createEvent('Event');
    event.promise = promise;
    event.reason = reason;
    event.initEvent(name, false, true);
    global.dispatchEvent(event);
  } else event = { promise: promise, reason: reason };
  if (handler = global['on' + name]) handler(event);
  else if (name === UNHANDLED_REJECTION) hostReportErrors('Unhandled promise rejection', reason);
};

Indeed, it seems in modern browser implementations global.dispatchEvent(event); calls the window.onunhandledrejection callback if the event type is unhandledrejection.

Two lines after, if (handler = global['on' + name]) handler(event); calls the exact same callback, as global == window and 'on' + name == onunhandledrejection.

Did I miss something? Is it a core-js bug?

[clemp6r]

I close the issue because this might have been caused by a hack we had to force usage of core-js Promise polyfill even on modern Browsers (delete window.Promise;).